Recent developments involving the use of laser technology in a variety of technical fields has created a corresponding need for improved laser systems. For example, a substantial amount of research has been conducted regarding the use of laser energy for medical purposes ranging from the treatment of dermatological conditions (described in U.S. Pat. No. 4,733,660) to the photocoagulation of blood vessels to control bleeding (described in U.S. Pat. No. 4,633,870 to Sauer). In particular, the medical use of laser technology has created a constant need for laser systems of compact size that have a high power to size/weight ratio.
For medical and other purposes, sealed gas lasers have been developed in which laser gas, such as carbon dioxide (CO.sub.2) or carbon monoxide (CO), in a resonator cavity is excited by radio frequency (RF) energy from an external source. A conventional RF-excited gas laser employs a resonator cavity having a square or circular discharge cross section, n example of which is shown in U.S. Pat. No. 4,169,251, issued to Laakman, which is incorporated by reference herein. This type of system is capable of significant output power and gas life, while maintaining a relatively small physical size. Conventional RF-excited lasers typically deliver about 0.8 to 1 W per linear inch of discharge length. Lasers over about 30 W of power typically fold their laser beams one to three times to maintain a reasonable length laser.
More recently, a second type of RF-excited gas laser known as a slab laser has been developed and is described in U.S. Pat. No. 4,719,639 to Tulip. Slab lasers include a pair of cooled metal electrodes having highly reflective surfaces with an oblong rectangular resonator cavity between the surfaces. Slab lasers can deliver more power per discharge length than conventional RF-excited gas lasers by using an oblong rectangular discharge cross section.
It is well known in the art that laser output power is increased by increasing the length in which the laser beam propagates. Because power and length of the discharge tube are related, the conventional approach to producing a small laser uses a folded structure to increase the effective length of the discharge tube. This results in relatively complicated optics assemblies and difficult alignment, in addition to possibly more complex discharge structures. It has been the inventor's experience that folding relatively short discharge sections is very inefficient because of low gain per section and relatively high turnaround losses.
For many applications in the medical and engraving field a power of 10 to 15 Watts is sufficient. For these applications, the conventional square- or circular-bore RF-excited technology has been the mainstay. In these applications, the laser is usually hard mounted (i.e. not handheld) and the beam is delivered through optical fibers, articulating arms or moving mirrors.
Notwithstanding previous developments in the field of laser technology (especially with respect to RF-excited sealed gas lasers), a need remains for a laser system of greatly reduced size that is nonetheless capable of producing high output power levels without the use of complex, intricate optical sub-systems. This laser must be economical to produce and be rugged. This rules out the complex prior art slab laser technology that is thought to be more suitable for high-powered metal cutting lasers.